The coil is rated to handle continuous 24V. on its coil (read 24/7), without overheating.
Because of the distance from the coil core, the voltage has to be approaching 18V. (this is the maximum voltage at which changeover occurs) on the coil to attract the armature. But having now closed the gap between armature and coil core, it stays there until the voltage on the coil reduces to not less than 2.4V. Then the armature releases.
This all relates to ANY relay, not just DPDT. However pull in and drop out voltages can change, you only have the data for 1 particular relay make and configuration.
In the end, you use 24V. on the coil. In most circuits there will be no voltage when the armature releases, but in some electronically switched voltages, some voltage can remain on the coil, which is why in this case it must not exceed 2.5V., or the relay armature will not release. The relay remains ON when it should have moved to OFF.